It has heretofore been a problem to incorporate benzidine in aramids without handling the monomer, a known carcinogen, The present process facilitates incorporation of such monomer into the polyamide chain by use of certain substituted benzidines. After the polyamide has been shaped, i.e., in the form of a fiber of film, the substituent may be driven off by pyrolysis. Certain of the polymers of the invention are capable of significant fiber tenacity increase on tensioned heat-treatment.